I wouldn't say the D800 has the same build as the D700, but it definitely has better image quality on every metric, and it weighs noticeably less, and it is every bit as responsive.

Don't be rough with it, use something like a BlackRapid strap attached directly to the tripod collar of heavier lenses, and if you can find a way of living with the capture rate (which, after all, is still pretty high by historical standards) you have an incredibly versatile camera.